Substantially constant time delay fishing jar

ABSTRACT

A fishing jar for removing stuck objects from a well bore wherein an upward strain on the running string compresses hydraulic fluid in a compression chamber to the amount of the upward jar or impact load desired to be applied to the fish stuck in the well including a movable piston means having a substantially constant flow regulator by-pass means therein to pass or transfer the compressed hydraulic fluid from one end to the other end of the piston means in the compression chamber. The piston means also includes seal means which define cross sectional areas adjacent each end of the piston means that are of different sizes and are responsive to the compressed hydraulic fluid to move it through the constant flow regulator by-pass means in the piston means, and thereby move the piston means in the compression chamber at substantially a constant rate to contact and open a valve which substantially instantaneously releases the compressed hydraulic fluid through a by-pass passage means so that a jar or impact is applied to the fish. The cross sectional areas formed by the seal means are of a predetermined size relative to each other, to thereby control the pressure differential of the compressed hydraulic fluid acting through the substantially constant flow regulator by-pass means, and to maintain such pressure differential within a predetermined range regardless of the load applied to the fish, within the design limits of the jar. Regardless of the hydraulic pressure in the compression chamber due to the jar load to be applied to the fish, the constant flow regulator by-pass means conducts substantially the same compressed fluid volume across the piston means at substantially the same rate so long as the pressure differential is within the predetermined range. Thus, the time delay to actuate the jar is relatively short and constant and is independent of downhole temperatures and pressures, or jarring loads, within the design limits of the tool.

United States Patent [1 1 Berryman Primary Examiner-James A. LeppinkAttorney, Agent, or Firm-Jack W. Hayden [57] ABSTRACT A fishing jar forremoving stuck objects from a well bore wherein an upward strain on therunning string compresses hydraulic fluid in a compression chamber tothe amount of the upward jar or impact load desired to be applied to thefish stuck in the well including a movable piston means having asubstantially constant flow regulator by-pass means therein to pass ortransfer the compressed hydraulic fluid from one end to the other end ofthe piston means in the compression chamber. The piston means alsoincludes seal means which define cross sectional areas adjacent each endof the piston means that are of different sizes and are responsive tothe compressed hydraulic fluid to move it through the constant flowregulator by-pass means in the piston means, and thereby movethe pistonmeans in the compression chamber at substantially a constant rate tocontact and open a valve which substantially instantaneously releasesthe compressed hydraulic fluid through a by-pass passage means so that ajar or impact is applied to the fish.

The cross sectional areas formed by the seal means are of apredetermined size relative to each other, to thereby control thepressure differential of the compressed hydraulic fluid acting throughthe substantially constant flow regulator by-pass means, and to maintainsuch pressure differential within a predetermined range regardless ofthe load applied to the'fish, within the design limits of the jar.

46 Claims, 7 Drawing Figures SUBSTANTIALLY CONSTANT TIME DELAY FISHINGJAR SUMMARY OF THE INVENTION Various types of fishing jars are employedfor removing some tool or tubular member or other object from a wellbore in the earth. The object stuck in the well bore is commonlyreferred to as a fish and fishing jars are run at the lower end of astring of drill pipe or tubing which ordinarily is referred to as thefishing, running or working string and the fishing tool is engaged withthe lower end thereof. The fishing tool may be a spear, or overshot orsimilar device adapted to engage the fish so that the fish may be jarredloose by the jar and thereafter retrived from the well bore.

Jars are employed for the purpose of applying hammer blows to aid inreleasing the stuck fish while the fishing string is under tension. Jarsof the hydraulic type, in general, are quite well known and comprisetelescoping members. When telescoped a pressure chamber containing aquantity of hydraulic fluid resists elongation of the jar. However, whenan upward strain or tension is applied to the running string, thehydraulic fluid is compressed and bleeds through a restricted flowpassage thus permitting a gradual telescoping of the tool until a largeby-pass is opened and the induced pressure on the hydraulic fluid isinstantaneously released. Since the fishing string is no longer resistedby the compressed fluid, the jar telescopes rapidly until suchtelescoping is stopped by engagement of a hammer and anvil that formpart of the fishing tool which applies a jar to the fish.

Fishing jars presently employed can deliver various amounts of upwardimpacts or jarring loads to the fish; however, with all fishing jarspresently known to applicant, the time delay from the time of placing atension on the fishing string to compress the hydraulic fluid until thetime that the fluid is by-passed or released so that an upward impact orjar may be applied by the fishing tool to the fish will varyconsiderably depending on the load to be applied.

When multiple hammerblows are to be successively applied to'the fish,the operation of jars may be time consuming since the by-passing orbleeding of the hydraulic fluid through a restricted passage causes atime delay depending upon the magnitude'o'f the tension which is appliedto the fishing string, and the magnitude of tension of the fishingstring determines the jarring load to be applied to the fish. Thus, ifthe jarring load is low, say for example 15,000 pounds, a comparativelylong period of time is required for the flow of hydraulic fluid throughthe restricted passage. Where higher jarring forces say for example,60,000 pounds are employed, the oil flows more rapidly through therestricted passage due, to the higher tension applied to the feet suchjar in a predetermined time range and if it is then desirable to jar at60,000 pounds, the jar may trip prematurely before the 60,000 pound jaris applied to the jarring tool.

Thus, if the operator desires to initially apply a low jar, say 20,000pounds, it is generally necessary to withdraw the running string and jarfrom the well bore and readjust the jar at the earths surface where ahigher jar, such as 60,000 pounds, is desired. The running string mustthen be again lowered into the well bore, all of which involves time andexpense.

On the other hand, if the jar is initially adjusted for a higher jarringforce, say 60,000 pounds, much time is consumed if it is then desired tojar at a lower force.

Other jars have no adjustment.

Still another disadvantage of hydraulic jars with which applicant ispresently familiar is that generally the metering stroke may vary from 2inches to 7 inches and the substantial volume of liquid is metered at avery high pressure. It can be appreciated that hydraulic jars of presentconstruction which require metering a hydraulic volume through a piston,or by-pass, under high differential pressure causes substantial heatbuild up. This in turn causes seal failures and where the jar isemployed over an extended period of time, the excessive heating of thehydraulic fluid reduces its viscosity and causes premature tripping ofthe jar before the desired load is placed on the fishing string at theearths surface.

From the foregoing, it can be appreciated that with hydraulic jarspresently employed, the tripping mechanism is sensitive or responds tothe load to be applied, and the smaller the load the slower the trippingmecha nism is in functioning. I

The present invention overcomes the above and other problems presentlyencountered in hydraulic fishing jars.

One object of the present invention is to provide a hydraulic jarwherein the tripping or actuating mechanism is not responsive ordependent upon the amount of load.

One object of the present invention is to provide a hydraulic jarwherein the tripping or actuating mechanism is not responsive ordependent upon the amount of load and which is constructed and arrangedto actu ate or trip at a relatively constant, short time regardless ofthe jarring load.

An object of the present invention is to provide a hydraulic fishing jarwhich does not depend upon metering the hydraulic fluid under highdifferential pressures,

thus sustaining negligible heat buildup.

fishing string and resulting greaterpressure differential Some jarspresently available are adjustable to vary 'the release time, althoughsuch adjustment is generally good only for a small range of jarringforces. For exam-- ple, if it is desired, by way of example only, to jarat 20,000 pounds, the prior art devices are adjusted to ef- Yet afurther object of the present invention is to provide a hydraulicfishing jar which has a constant time delay regardless of the loadapplied to the fishing jar within the range of .the design limitationsof the particular size jar.

Still another object of the present invention is to provide a constanttime delay fishing jar wherein the upward impact applied by the jar tothe fish occurs approximately ten to twenty seconds after the operatorstarts the jarring stroke, regardless of the load to be applied to thefish by the jar, regardless of downhole temperatures and pressures andwithin the design limits of the jar.

Yet a further object of the present invention is to provide a fishingjar for removing stuck objects from a well areas in the chamber of adifferent size which are responsive to the compressed hydraulic fluidfor passing the compressed hydraulic fluid through a constant flowregulator by-pass means in a piston to effect movement of the piston toopen a valve and release the compressed hydraulic fluid through a bypassso that a jar may be applied to the fish.

Yet a further object of the present invention is to pro vide a fishingjar for removing stuck objects from a well bore in whichhydraulic fluidwithin a compression chamber is compressed by a piston to the jar loaddesired to be applied to the fish without requiring any initial settingby an operator at the earths surface, or any adjustment of the hydraulicjar once it is in operation and wherein such jar includes spaced crosssectional areas in the chamber of a different size which are responsiveto the compressed hydraulic fluid for passing the compressed hydraulicfluid through a constant flow regulator by-pass means in a piston toeffect movement of the piston to open a valve and release the compressedhydraulic fluid through a by-pass so that a jar maybe applied to thefish, said spaced cross sectional areas being a predeterminedrelationship for controlling the compressed hydraulic fluid pressuredifferential in the chamber acting through the-constant-flow regulatormeans to move the piston at a constant rate with a minimum of pressuredifferential in the compression chamber acting through the constant flowregulator means and with a minimum metering stroke of the jar from aminimum jar load to a maximum jar load for which the fishing jar isdesigned.

Yet a further object of the present invention is to provide a hydraulicfishing jar which eliminates the substantial time delays presentlyencountered with hydraulic jars.

Still another object of the present invention is to provide a hydraulicjar of relatively simple design wherein a minimum stroke is required tocompress hydraulic fluid in the hydraulic compression chamber to adesired load and thereafter meter such compressed fluid across arelatively 'small pressure differential as compared with prior arthydraulic jars with the time for compression to any desired load andtripping to apply an impact requiring a minimum and relatively constantamount of time such as ten to twenty seconds.

Still another object of the present invention is to provide a hydraulicjar of relatively simple construction which should be normallysubstantially foolproof to apply any desired load to a fish with thetime delay at any load being substantially the same as at any otherload.

Other objects and advantages of the present invention will becomeapparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A through 1C togetherconstitute generally a longitudinal partial quarter section of a jarringtool of the preferred form of the present invention installed in afishing string and illustrates the position of the components when thetool is in a collapsed or telescoped relation;

FIGS. 2A through 2C together constitute a fragmentary, generallylongitudinal quarter section through portions of the jarring toolillustrated in FIGS. 1A through 1C, FIGS. 2A through 2C illustrating thecomponents when the tool is extended and at the moment that an upwardimpact is delivered to the fish; and

FIG. 3 is a fragmentary sectional view showing a check valve meansmounted in the piston means.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hydraulic fishing jar of thepresent invention is referred to in FIG. 1A generally by the numeral 5.It comprises an elongated tubular inner mandrel or body 6 and an outertubular elongated body or housing 7. The inner body 6 at its upper endis provided with a threaded box 8 of well known configuration which isadapted to receive the externally threaded pin 9 at the lower end of theupwardly extended section of drill pipe or drill collar or other tubularmember I consituting a portion of the running or fishing string on whichthe jar is run into the well bore, and by which the jarring tool isoperated to provide a jarring action for a fishing tool which may bedesignated F connected to the threaded end 13 on the lower end of theouter housing or body 7 as more clearly seen in FIG. 1C.

The inner housing or body 6 is provided adjacent its upper end with aplurality of elongated circumferentially spaced grooves 15 havinglongitudinally extending projections 16 extending between the grooveswhich elongated, circumferentially spaced grooves 15 are adapted toreceive the circumferentially spaced projections 18 formed on theannular member 20 adjacent the upper end of the outer body or housing 7.The circumferentially spaced projections 18 are provided with elongatedrecesses therebetween illustrated at 22 for receiving the elongatedcircumferentially spaced projections 16 on the inner body 6.

This arrangement provides a splined configuration for enabling th innerbody 6 and outer body 7 to telescope longitudinally relative to eachother while inhibiting relative rotation therebetween.

It can be appreciated that the grooves 15 and projections 16 will be ofany suitable or longitudinal extent to accommodate the desiredtelescoping movement of the inner body 6 and outer body 7 forcompression of the hydraulic fluid in the compression chamber and forrelease thereof to enable an upward blow to be delivered to the fish ina manner as will be described in greater detail.

An annular member 26 is secured on the body 6 below the splinearrangement hereinbefore described by means of the threads 24 formed onthe inner body 6 and threads 25 formed on the annular member 26. Also ifdesired such member may be further secured in place by the threaded pin28 extending through the member 26 and into a suitably threaded opening29 in the inner body 6.

The upper annular end 26a of the member 26 forms the hammer fordelivering an upward impact when the inner body 6 is released relativeto the outer body 7 as will be described.

The inner body 6 comprises a plurality of longitudinally tubularportions secured together including the portion 6a and to which issecured the tubular, longitudinally extending portion 6b by suitablemeans such as the cooperating threads on 6a and 6b referred to at 60.

A suitable seal 31 is interposed between unthreaded portions of thecylindrical surfaces of 6a and 6b for sealing therebetween. Threadedlysecured to the lower end of the tubular section 6b is the tubularsection 6a' which forms the lower end of the inner tubular body orhousing 6. Suitable cooperating threads referred to generally at 62formed on the tubular inner body por-- tion 6d and tubular inner bodyportion 6e enable them to be threadedly connected together and suitableseal means as shown at 32 are provided between the unthreaded portionsof the cylindrical surfaces of the members 6b and 6d for-sealingtherebetween.

The outer tubular body or housing 7 includes the uppermost tubularportion 7a on which are formed the circumferentially spaced projections18 with the recesses 22 therebetween as previously described. The lowerannular end 30a on member forms an anvil against which hammer 26astrikes to deliver a jar as will be described. The upper outer bodyportion 7a threadedly connected to the next adjacent outer tubular bodyportion 7b by suitable cooperating threads referred to generally at 70formed on the lower end of 7a and at the upper end of 7b as shown inFIG. 1A of the drawing. The portion 7b includes the upwardly extendingannular projection 7d which is threadedly engaged with the annularmember 7e by means of the threads referred to generally at 7f formed onthe extension 7d and the annular member 7e as shown in FIG. 1A. It willbe noted,

that the annular member 72 surrounds and slidably engages the innertubular body 6 and more particularly the tubular body portion 6b asshown in FIGS. 1A and 2A of the drawings.

Suitable seal means comprising the annular seal rings 35 and 36 arepositioned on the shoulder 38 of the member 7b adjacent the cylindricalsurface 39 of the member 6b and are retained in position by the annularmember 72 and retainer 40. The seal means 35 and 36 provide means whichdefine the upper end of a hydraulic fluid chamber referred to generallyat 45 in the drawings. Such chamber extends longitudinally from the sealmeans 35, 36 between the inner body 6 and outer body 7 to the seal means42 and 43 carried in the annular floating piston 44 at the lower end ofthe jar 5 in the annular space between the inner body 6 and the outerbody 7 as shown in FIG. 1C. Suitable openings 0 are provided for fillingchamber 45 and bleeding air therefrom as such filling occurs. The plugsP may then be threadedly engaged in the openings 0, with a suitable sealring S thereon to prevent loss of fluid.

The outer tubular body portion 7b is connected to the outer tubular bodyportion 7g by suitable means such as the cooperating threads formed onthe lower end of the outer body portion 7b and the upper end of theouter body portion 7g, which cooperating threads are referred togenerally by the numeral 7h. Suitable seal means 46 are provided betweenthe unthreaded cylindrical surfaces of the members 7b and 7g to inhibitleakage therebetween. The outer tubular body portion 7g is connected atits lower end to the outer tubular body portion 71' by suitable meanssuch as the cooperating threads adjacent the lower end of the outertubular body portion 7g and the. upper end of the outer tubular bodyportion 71', such threads being referred to generally by the numeral 7j.Suitable seal means as shown at 48 are provided between the unthreadedcylindrical surfaces of the outer tubular body portions 7g and 7i toinhibit leakage therebetween.

As previously noted the threaded end 13 of the outer tubular body 71'provided for connecting with the fishing tool F of a suitable type.

Power piston means are referred to generally at 55 and include theannular element 55 and the annular enlargement 57 on body portion 6g,which cooperate to provide a valve arrangement in the power piston 55 aswill be described. The annular element 55 is between'the outer body 7and inner body portion 6g and is spaced radially from the outer surfaceof 6g to form a flow passage 6g therebetween as shown in FIG. 1C whenthe element 55 is spaced from enlargement 57. The element 55 issupported on the annular shoulder 56 formed in outer body portion 7g.Suitable seal means 55a seal between element 55 and the innercylindrical wall of housing 7. The annular element 55 of power piston 55is retained in position on the shoulder 56 when the jar of the presentinvention is in the collapsed position shown in FIGS. lA-lC by means ofthe spring 58 extending longitudinally of the chamber 45. The spring atits upper end abuts an annular shoulder on the lower end of piston meansreferred to generally by the numeral 60, which piston means also isslidably mounted within the chamber 45 as shown in FIGS. 18 and 2B.-

The piston means 60 includes piston valve means 65, substantiallyconstant flow by-pass means referred to generally at 61 and the passagemeans 62 for by-passing fluid across the piston means 60 in a manner aswill be described. The piston means 60 also includes one-way actingcheck valve means 61d as shown in FIG. 3 which is carried in passagemeans 62a in annular piston means 60 at a position circumferentiallyspaced relative to constant flow by-pass means 61. The check valve means61d functions as will be described to flow fluid from compressionchamber 101 to 100 beneath piston means 60.

The annular piston valve means referred to at 65 is provided with anannular surface 66 for sealably engaging with the upper end 68 of thepiston means 60 as illustrated'in FIG. 1C of the drawings. The pistonvalve means 65 includes a plurality of circumferentially spaced flowports 67 formed in the annular projection 67a which when the pistonvalve means 65 is seated on the end 68 of piston means 60 extends beyondthe end 68 of piston means 60 and between such piston means and bodyportion 6b. This prevents communication of ports 67 with chamber portion101. The piston valve means 65 is urged towards seated position on theupper end 68 of the piston means 60 by means of the resilient means 69which abuts the shoulder 70 on the outer housing body portion 7b at oneend, with its other end resting on the end 65a of the valve means 65.The annular valve means 65 is slidably arranged on the inner body 6 andmore specifically the inner body portion 6b lar upwardly extendingannular skirt 6g which skirt thus is part of inner body 6 and extendslongitudinally of, and surrounds the lower most inner body portion 6b asshown in FIGS. 1B and 1C of the drawings.

The upper end 6h of the extension 6g terminates in spaced relation tothe annular shoulder 81 formed on the valve member 80 as shown in FIG.1B and thevalve member 80 is slidable relative to the upwardly extendingbody portion 6g as shown in FIGS. 18 and 1C. Suitable seal means asshown at 81a are provided between the cylindrical surface of 6g and thevalve member 80 so that the valve member 80 is thus sealably andslidably carried by the inner body 6. v

The upper end 83 of the valve member 80 seats against the lower end 84of the annular skirt means 85 mercially, it is not deemed necessary togive a detailed description as it is well known to those skilled in theart.

It can be appreciated that a constant flow regulating valve responsiveto a different range of pressure differentials and a different constantflow rate may be employed, and the foregoing is given by way ofillustration only.

In order to maintain the proper hydraulic pressure differential betweencompression chamber 100 and compression chamber seal means are providedin the chamber 45 between the piston valve means 65 and said inner body6 and between said piston means 60 and the outer body 7g and between thepiston means 60 and means 85 to provide cross sectional areasrespectively adjacent each end of the piston means in the compressionchamber 100 and compression chamber which is secured by any suitablemeans such as threads 86 or the like to the tubular portion 6d of theinner body 6 and thus forms a part of the inner body 6.

When the components of the jar of the present invention are in therelative position as shown in FIGS. 1A through 1C, it will be noted thatthe resilient means 88 supported on the shoulder 89 of the annular skirt6g engages the annular shoulder 90 on valve member 80 to urge the valvemember 80 upwardly into sealing contact with the lower end 84 of theannular skirt means 85 and to maintain 57 in spaced relation to element55' when the inner and outer bodies of the tool are collapsed relativeto each other.

It will be further noted that by-pass flow passage means 61a extendsfrom immediately above the end' 85a of the means 85 and extendslongitudinally therebeneath as well as beneath the annular skirt 6gcarried on inner body portion 6d so as to communicate with the lower endof the chamber 45 through the port means 91 formed in skirt 6g beneathpower piston 55 as shown in FIG. 1C.

Suitable seal ring means 96 are provided between the annular pistonmeans 60 and the outer body 7 and additional seal ring means 97 areprovided between the piston means 60 and inner body 6. It will be notedthat the seal 96 sealably and slidably engages the inner cylindricalsurface of the outer body portion 7g while the seal 97 engages the outercylindrical surface of the means 85 secured to and forming part oftheinner body 6.

By way of example only the constant flow regulating means referred togenerally at 61 includes a substantially constant flow regulating valve61c of well known configuration which will transfer compressed hydraulicfluid from the hydraulic compression chamber 100 to the hydrauliccompression chamber 101 at substantially a'constant flow rate so long asthe pressure differential of the hydraulic fluid between compressionchamber 100 and compression chamber 101 is within a predetermined range.By wayof example only, when the pressure differential between chambers100 and 101 is greater than approximately 50 p.s.i. differential, butless than approximately 3,000 p.s.i. differential, the flow rate fromchamber 100 to chamber 101 is constant at 0.3 gallons per minute. Sincesuch flow regulator is of well known construction and may be obtainedcom- 101 which are responsive to the compressed hydraulic fluid forpassing the compressed hydraulic fluid through said constant flowby-pass means 61 at substantially a constant rate and with a minimumpressure differential for any load applied to the jar.

More particularly, the-seal means 71 in the annular piston valve means65 which engages inner body portion 617 and the seal means 96 betweenthe piston means 60 and outer housing portion 7g define one effectivecross sectional area adjacent one end of the piston means 60 responsiveto compressed hydraulic fluid within the compression chamber 101 andwhich is illustrated at A1, in FIG. 1B. Similarly, seal means 96 betweenthe piston means 60 and outer housing portion 73 and seal means 97between the piston means 60 and the means 85 define an effective crosssectional area illustrated at A2 adjacent the other end of the pistonmeans 60 responsive to compressed hydraulic fluid in compression chamber100. The jar is designed and constructed so that cross sectional area Aldefined by the seals 71 and 96 is larger than the crosssectional area A2defined by the seals 96 and 97.

When hydraulic fluid is compressed in the chamber between the inner body6 and'outer body 7, the forces acting on the piston means 60 will tendto balance, and the hydraulic pressure in the compression chamber 100beneath the piston 60 is greater than that in compression chamber 101above the piston means 60 by the ratio of A1 divided by A2. Thus, when aload is applied to the hydraulic column in chamber 45 by the innertubular member and power piston to compress the hydraulic fluid, fluidwill be displaced from the compression chamber 100 to the compressionchamber 101 i through the constant flow regulator means 61 carried bythe piston 60.

As fluid is displaced from beneath the piston means 60 to the top of thepiston means 60, the piston means 60 will travel downwardly at a fixedrate of travel in the compression chamber portion 100.

When piston means 60 engages valve member and moves it off the seat 84,compressed hydraulic fluid from chamber 100 is discharged throughby-pass flow passage 61a to chamber portion 45a beneath power piston 55.Release of the compressed hydraulic fluid permits the inner mandrel 6 tomove upwardly until the end a of means 85 engages the lower end 65b ofvalve means 65 and moves it away from piston means 60, so thatcompressed fluid from chamber 101 is conducted to by-pass 61a. The innerbody 6 continues its upward movement so that hammer 26a strikes anupward blow on anvil 30a.

Description of Operation While it is believed that the operation of thepresent invention is apparent by the reason of the foregoing, to furtheramplify and describe, attention is now directed to FIGS. 2A through 2Cof the drawings.

In such views, the components of the jar 5 of the present invention areshown in their relative position at the time that an upward jarring blowis delivered by the jar to a fish engaged by fishing tool F.

In order to deliver an upward jarring blow to a fish in a well bore, thefishing tool F is first engaged with the stuck fish when the operatingstring is lowered into the well bore.

Thereafter an upward strain is taken on the fishing or operating stringat the earths surface in a desired amount. For example, in a tool of thepresent design of 4 inches outer diameter of the outer tubular body 7,the maximum load or jar that may be'applied to a fish is 55,000 poundsdue to the physical limitations and strength of the materials involved.However, any desired load up to this amount may be applied by thepresent invention without any adjustment at the earths surface or in thewell bore. There is a relatively constant time delay from the time thatthe desired load is applied by the fishing string until the jar isreleased to deliver an impact to the fish whether the jarring loadapplied is 15,000 or 554000 pounds and the relatively constant timedelay is independent of downhole temperatures and pressures.

As an upward strain or pull is applied at the earths surface to thefishing string illustrated in FIG. 1A of the drawings, this istransmitted through the inner body 6 and its body portions previouslydescribed. The outer body 7 will remain stationary since it is connectedby its respective outer body portions to the fishing tool F which inturn is secured to the fish to which the upward jarring impacts are tobe delivered.

Upward movement of the inner body 6 including body portions 6a, 6b, 6d,and 6g moves the shoulder 6g on enlargement 57 into sealing engagementwith the lower end 55a of annular element 55'. When 57 and 55' are thussealingly engaged, passage 6g is closed off and the power piston meansformed by 57 and 55 compresses the hydraulic fluid in compressionchambers 100 and 101, since chamber 45 referred to as 45a beneath powerpiston 55 is isolated from the compression chamber, includingcompression chambers 100 and 101 on each end of piston means 60. Thus,the desired jarring load is transmitted to the hydraulic fluid withinsuch compression chamber defined by chambers 100 and 101 to compress it.

If it is desired to apply a jarring load of 20,000 pounds to the stuckfish, then the operating string will be pulled at the earths surface tocompress the hydrau lie fluid by power piston means 55 in jar 5 untilthe weight indicator at the earths surface indicates that such load ispresent in the compressed hydraulic fluid, of course, such weightindicator indicating the 20,000 pounds load plus the weight of theworking string in the well bore.

means 60 and A2 on the other side of the piston means 60, there will bea greater hydraulic pressure per unit area beneath the piston means 60in compression chamber 100 than above piston means 60 in compressionchamber 101 so that hydraulic fluid flows through the constant flowregulator means 61 in piston means 60 to the compression chamber 101above the piston from chamber 100.

The flow of hydraulic fluid across piston means 60 is at substantially aconstant rate due to the constant flow regulator by-pass means 61 andthe piston means 60, by reason of the hydraulic fluid flow to the topside thereof, moves downwardly and spring 58 yields as the piston means60 moves relative to power piston means 55. The movement of piston means60 is at substantially a constant rate until its lower end 60a tags thetop 83 of the valve member 80. At the time that the piston means 60contacts the top 83 of the valve means there will still be a pressuredifferential between compression chamber 101 and compression chamber 100and compressed hydraulic fluid will continue to flow from compressionchamber 100 to compression cham her 101. However, since the effectivecross sectional area A1 in pressure chamber 101 is larger than theeffective cross sectional area A2 in pressure chamber 100 the additionalfluid flow from hydraulic compression chamber 100 through constant flowregulator means 61 to compression chamber 101 causes piston means 60 tomove further downwardly and move the top 83 of valve means 80 away fromthe lower end 84 of means 85. When this occurs, by-pass flow passage61a'is communicated with compression chamber 100 by means of the annularspaced port means 60b immediately adjacent the lower end 60a of pistonmeans 60 and dumps the compressed fluid in chamber 100.

This permits the inner body 6 along with power piston 55 to moveupwardly substantially instantaneously relative to the outer housing 7since the compressed hydraulic fluid from compression chamber 100 isdumped by the bypass flow passage 61a and ports 91 in 6g to the chamberportion 450 beneath the power piston 55. The upward movement of innerbody portion 6 along with power piston 55 at the time that by-pass flowpassage 6la communicates with compression chamber 100 moves the upperend 6h of 6g from the position shown in FIG. 18 to the position shown inFIG. 28 so that end 6h engages shoulder 81 of valve member 80. Theupward movement of inner body 6 also moves means from the position shownin FIG. 18 to the position shown in FIG. 28 so as to contact the upperend 85a of the means 85 on inner body 6 with the lower end 65b of thepiston valve means 65 and thereby unseat it from engagement with theupper end 68 of piston means 60.

It should be noted that as piston means 60 moves in the compressionchamber, valve means 65 remains in sealing engagement with the upper end68 of piston means 60 until means 85 engages its end 65b and unseats it.

When this occurs, compressed hydraulic fluid from compression chamber101 flows to by-pass means 61 through annular spaced port means 67 invalve means 65 as shown in FIG, 2B.

As previously noted, once communication is established betweencompression chamber and fluid bypass flow passage 61a, the upwardrelative movement of inner body 6 relative to outer housing or body 7 isrelatively sudden and the inner body 6 continues its rapid, upwardmovement so that hammer 26a strikes a blow against anvil 30a.

To further illustrate the operation of the present invention on a 4 4inch O.D. tool, the cross sectional area at A2 may preferably be 4.643square inches and the cross sectional area of A1 may preferably be 5.409square inches. When a load of 20,000 pounds is applied by the operatingstring as described in the above example, the pressure in compressionchamber 100 will therefore be approximately 4,310 pounds per square inchand the pressure in compression chamber 101 piston means 60 will beapproximately 3,700 pounds per square inch, thus yielding a pressuredifferential of only 610 pounds per square inch between cross sectionalarea A2 and cross sectional area A1.

By way of further example, if a load of 50,000 pounds is desired to beapplied to the fish, then the inner body is again tensioned upwardlyuntil the weight indicator at the earths surface indicates that suchload plus the weight of the fishing string is applying a 50,000 poundload in the hydraulic compression chambers 100 and 101.

Under these conditions the effective cross sectional area A2 incompression chamber 101 has a pressure of approximately 11,200 poundsper square inch applied thereto and the pressure in compression chamber101 acting on the effective cross sectional area A1 is approximately9,250 pounds so that the pressure differential is approximately only1,950 pounds per square inch even though the jarring load is 50,000pounds.

It should be noted that valve member 80 is constructed and arranged sothat it is biased towards closed position against the end of means 85 asshown in the drawings, but as long as the difference in cross sectionalareas A1 and A2 is substantially greater than the biased area of valvemember 80, the piston means 60 will overcome the spring force 88 andbias of the valve member 80 to open it as described It can beappreciated that floating piston 44 is a pressure compensating piston toequalize the pressure in chamber 45 with the pressure in the fishingstring since the underside of the piston 44 is exposed to the pressurepresent in the running or fishing string 10.

In addition to a substantially less pressure differential during themetering cycle in the present hydraulic jar as compared with priordevice which normally meter at the full differential of the jarringload, substantially less travel of the inner body 6 relative to outerbody 7 occurs during the metering cycle, that is during the period thathydraulic fluid is conducted from compression chamber 100 throughconstant flow regulator by-pass means 61 to compression chamber 101.

Piston means 60 travels downwardly during the metering cycle when fluidis displaced upwardly through the constant flow by-pass means 61 asdescribed previously. Since cross sectional area Al in compressionchamber 101 is larger than the cross sectional area A2 in compressionchamber 100, the volume in compression chamber 1011 opened up by thedownward movement of piston means 60 will be larger than that displacedbelow the piston means 60 as it moves downwardly. To compensate for thisthe inner body 6 will move upwardly relative to outer housing 7 to makeup for this difference in volume and the amount it will move up equalsthe stroke of the piston means 60 relative to inner body 6 times thedifference between the cross sectional areas Al and A2 divided by thecross sectional area A1.

As mentioned previously on a 4 inch OD. tool, the cross sectional areaA1 in the example is 5.409 square inches and the cross sectional area A2in the example is 4.643 square inches and the stroke of the piston meansis 4 inches. Therefore the total metering stroke of the presenthydraulic jar is 5.409 minus 4.643 divided by 5.409 times 4 which equals0.567 inches. Thus the metering stroke of the, device of the presentinven tion is relatively small compared with prior art devices.

The amount of heat generated in a hydraulic jar is proportional to theload applied times the metering stroke of the jar. Thus, it can beappreciated that the amount of heat generated by the hydraulic jar ofthe present invention would be 0.567 divided by 7, or approximately l/l2that of the conventional hydraulic jars at the same load, assuming thatsuch conventional hydraulic jar has a stroke of 7 inches during themetering cycle of the compressed hydraulic fluid.

After the tool has been actuated, the inner and outer bodies may becollapsed or moved to the position shown in FIG. lA-lC. As this occurs,enlargement 57 moves away from element 55 and passage 6g" along withcheck valve means 61d and passage 61a enable hydraulic communication inthe chamber to be accomplished so that the tool components may bequickly and easily repositioned so that another jar may be applied. Theone-way check valve means 61d communicates, or passes fluid acrosspiston means 60 from the top thereof to the bottom thereof.

From the foregoing it is also seen that enlargement 57 and element 55not only cooperate to form the power piston means 55, but also cooperateto form a valve arrangement in the power piston means 55 for closing offflow therearound or for opening for flow across the power piston means55.

The construction and arrangement of the present invention overcomes theobjections of prior art hydraulic jars which meter hydraulic fluid atthe full pressure induced by the tensile load on the jar, whether it is20,000 pounds, 50,000 pounds or any other load, and thus overcomes theproblems of heat build up, seal failures, and premature tripping whichoften occur with conventional hydraulic jars presently known toapplicant.

Also, the travel of the inner body 6 during the metering stroke issubstantially less, as above noted, than that possible with hydraulicjars of present conventional design known to applicant. 4

Thus, the hydraulic jar of the present invention need only be assembledand filled with hydraulic fluid in chamber 45 and connected in fishingstring S for lowering into the well bore. After the fish is engaged bythe fishing tool F, any desired load may be applied to the jar, withinits design limits, and approximately ten to twenty seconds after tensionis initiated in the operating string as described herein, the jar willactuate and deliver an impact, the elapsed time being independent of themagnitude of the load and independent of well temperatures andpressures.

The present invention can be repeatedly employed and the jarring loadmay be varied, that is, increased or decreased as desired, while the jarremains in the well bore.

All of the foregoing is accomplished without any operator adjustment ofthe jar; nor is any presetting of the jar required before it goes intothe well bore, nor is any adjustment required once the jar is inoperation.

Also, as noted previously, since the tripping mechanism is not loadsensitive, and since the invention incorporates a constant time delaydesign, the jar of the present invention will trip ar actuateapproximately ten to twenty seconds after the operator begins thejarring stroke, regardless of the jarring load, within the design limitsof the tool.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape, and materials as well as in the details of the illustratedconstruction may be made without departing from the spirit of theinvention.

What is claimed is:

1. In a hydraulic fishing jaradapted to be run into a well on a fishingstring and connected to a fish in the well bore:

a. inner and outer telescopically interengaged bodies;

b. means defining between said bodies a hydraulic fluid chamber;

c. power piston means in the chamber operable upon tensioning thefishing string for telescopic movement of said bodies to compress andapply a predetermined force to the hydraulic fluid in the chamber;

d. therebeing bypass flow passage means in one of said bodies;

e. a valve member in the chamber for normally closing off one end of theby-pass flow passage means from the compressed fluid in the chamber andshiftable to open so that compressed hydraulic fluid is released to theby-pass flow passage means;

f. piston means including substantially constant flow by-pass means totransfer the compressed hydraulic fluid in the chamber across saidpiston means and thereby move it in the fluid chamber at substantially aconstant rate to engage and move said valve member'to open the by-passflow passage means at one end to the compressed hydraulic fluid;

g. said piston means including valve means normally closing off theother end of the bypass flow passage means and shiftable to open so thathydraulic fluid is released from the chamber above said piston means;

h. means on one of said bodies to move said piston valve means and openthe other end of the by-pass flow passage means when said valvemember'is moved to open one end of the bypass flow passage means to thecompressed-hydraulic fluid; and

. hammer and anvil means on said bodies movable into engagement whensaid valve member and piston valve means open the by-pass passage meansto the chamber across said piston means.

2. The invention of claim 1 wherein said piston means includes sealmeans sealably and slidably engaged in the chamber to provide crosssectional areas of different size on said piston means responsive to thecompressed hydraulic fluid in the chamber for transfer thereof acrosssaid piston means.

3. The invention of claim 2 wherein said cross sectional areas are of apredetermined relationship for controlling the compressed hydraulicfluid pressure differential across said piston means in the chamberacting to move said piston means.

4. The invention of claim 2 wherein said piston means is an annularmember having top and bottom ends and wherein the cross sectional areadefined by said seal means adjacent said bottom piston end is smallerthan the cross sectional area defined by said seal means adjacent saidtop piston end.

5. The invention of claim 1 including annular seat means formed on saidpiston valve means and said piston means for seating said piston valvemeans on said piston means.

6. The invention of claim 1 including resilient means normally urgingsaid piston valve means into sealing engagement with said piston meansuntil said means on one of said bodies engages said piston valve means.

7. The invention of claim 1 wherein said means on one of said bodies atone end thereof forms seat means for said valve member.

8. The invention of claim 7 including resilient means normally urgingsaid valve member into sealing engagement with said seat means untilsaid piston means moves said valve member off said seat means.

9. The invention of claim 1 including resilient means in the chamberurging said piston means away from said valve member and yieldable assaid piston means moves to engage said valve member.

10. The invention of claim 9 wherein said resilient means urging saidpiston means away from said valve member also engages said power pistonand is yieldable upon movement of said piston means relative to saidpower piston.

' 11. The invention of claim 1 wherein said means defining the hydraulicfluid chamber comprises upper and lower seal means between said bodies,one of said seal means being a floating piston for compensating for thepressure of fluid in the wellv 12. The invention of claim 1 wherein saidvalve member is slidably and sealably carried by said inner body.

13. The invention of claim 1 wherein said piston valve means is slidablyand sealably carried by said inner body.

14. The invention of claim 1 wherein said piston means is slidably andsealably carried in said chamber.

15. The invention of claim 1 wherein said by-pass flow passage means isformed in said inner body;

16. The invention of claim 2 wherein one of said cross sectional areasis defined by seal means between said piston valve means and inner bodyand seal means between said piston means and outer body, and the otherof said cross sectional areas is defined by seal means between saidpiston means and outer body and seal means between said piston means andinner body.

17. The invention of claim 2 wherein said cross sectional areas are of apredetermined relationship for maintaining the compressed hydraulicfluid pressure differential across said piston means within apredetermined range.

18. The invention of claim 1 wherein said substantially constant flowby-pass means, includes. substantially constant flow regulator meanswhereby the compressed hydraulic fluid moves therethrough atsubstantially a constant rate within the predetennined pressuredifferential range.

19. In a hydraulic fishing jar adapted to be run into a well on afishing string and connected to a fish in the well bore:

a. inner and outer telescopic bodies; b. meansincluding longitudinallyspaced seals defining between said bodies a hydraulic fluid chamber;

c. power piston means including an annular piston carried by one of saidbodies and shiftable longitudinally in said chamber by the other of saidbodies upon tensioning the fishing string for telescopic movement ofsaid bodies to compress and apply a predetermined force to the hydraulicfluid in the chamber;

d. therebeing by-pass flow passage means in one of said bodies; I

e. a valve member in the chamber for normally closing off one end of theby-pass flow passage means from the compressed fluid in the chamber andshiftable to open so that compressed hydraulic fluid is released to theby-pass flow passage means;

f. piston means including substantially constant flow by-pass means totransfer the compressed hydraulic fluid in the chamber across saidpiston means and thereby move it in the fluid chamber at substantially aconstant rate to engage and move said valve member to open the by-passflow passage means at one end to the compressed hydraulic fluid;

g. said piston means including valve means normally closing off theother end of by-pass flow passage means and shiftable to open so thathydraulic fluid is released from the chamber above said piston means;

h. means on said inner body to move said piston valve means and open theother end of the by-pass flow passage means when said valve member ismoved to open one end of the by-pass flow passage means to thecompressed hydraulic fluid; and

i. hammer and anvil means on said bodies movable into engagement whensaid valve member and piston valve means open the by-pass passage meansto the chamber across said piston means.

20. The invention of claim 19 wherein said piston means includes sealmeans sealably and slidably engaged in the chamber to provide crosssectional areas of different size on said piston means responsive to thecompressed hydraulic fluid in the chamber for transfer thereof acrosssaid piston means.

21. The invention of claim 20 wherein said cross sectional areas are ofa predetermined relationship for controlling the compressed hydraulicfluid pressure differential across said piston means in the chamberacting to move said piston means.

22. The invention of claim 21 wherein said piston means is an annularmember having top and bottom ends and wherein the cross sectional areadefined by said seal means adjacent said bottom piston end is smaller insize than the cross sectional area defined by said seal means adjacentsaid top piston end.

23. The invention of claim 19 including annular seat means formed onsaid piston valve means and said piston means for seating said pistonvalve means on said piston means.

24. The invention of claim 19 including resilient means normally urgingsaid piston valve means into sealing engagement with said piston meansuntil said means on said inner body engages said valve means.

25. The invention of claim 19 wherein said means on said inner body atone end thereof forms seat means for said valve member.

26. The invention of claim 25 including resilient means normally urgingsaid valve member into sealing engagement with said seat means untilsaid piston means moves said valve member off said seat means.

27. The invention of claim 19 including resilient means in the chamberurging said piston means away from said valve member and yieldable assaid piston means moves to engage said valve member.

28. The invention of claim 20 wherein said valve member is slidably andsealably carried by said inner body.

29. The invention of claim 27 wherein said resilient means urging saidpiston means away from said valve member also engages said power pistonand is yieldable upon movement of said piston means relative to saidpower piston.

30. The invention of claim 19 wherein said piston valve means isslidably and sealably carried by said inner body.

31. The'invention of claim 19 wherein said piston means is slidably andsealably carried in said chamber.

32. The invention of claim 19 wherein the bypass flow passage means isformed in said inner body.

33. The invention of claim 20 wherein one of said cross sectional areasis defined by seal means between said piston valve means and inner bodyand seal means between said piston means and outer body. and the otherof said cross sectional areas is defined by sea] means between saidpiston means and outer body and seal means between said piston means andinner body.

34. The invention of claim 20 wherein said cross sectional areas are ofa predetermined relationship for maintaining the compressed hydraulicfluid pressure differential across said piston means withina'predetermined range.

35. The invention of claim 19 wherein said substantially constant flowby-pass means, includes substantially constant flow regulator meanswhereby the compressed hydraulic fluid moves therethrough atsubstantially a constant rate within the predetermined pressuredifferential range.

36. In a well bore fishing string hydraulic fishing jar having inner andouter telescopically interengaged bodies with a hydraulic fluid chambertherebetween I and power piston means in the chamber to compress fluidis released to the bypass flow passage means;

c. piston means includingsubstantially constant flow by-pass means totransfer the compressed hydraulic fluid in the chamber across saidpiston means and thereby move it in the fluid chamber at substantially aconstant rate to engage and move said valve member to open the by-passflow passage means at one end to the compressed hydraulic fluid;

d. said piston means including valve means in the chamber normallyclosing off the other end of the by-pass flow passage means andshiftable to open so that hydraulic fluid is released from the chamberabove said piston means; and

e. hammer and anvil means on said bodies movable into engagement whensaid valve member and piston valve means open the by-pass passage meansto the chamber across said piston means.

37. The invention of claim 36 wherein said piston means includes sealmeans sealably and slidably engaged in the chamber to provide crosssectional areas of different size on said piston means responsive to thecompressed hydraulic fluid in the chamber for transfer thereof acrosssaid piston means.

38. The invention of claim 37 wherein one of said cross sectional areasis defined by seal means between said piston valve means and inner bodyand seal means between said piston means and outer body, and the otherof said cross sectional areas is defined by seal means between saidpiston means and outer body and seal means between said piston means andinner body.

39. The invention of claim 37 wherein said cross sectional areas are ofa predetermined relationship for maintaining the compressed hydraulicfluid pressure differential across said piston means within apredetermined range.

40. The invention of claim 36 wherein said substantially constant flowby-pass means, includes substantially constant flow regulator meanswhereby the compressed hydraulic fluid moves therethrough atsubstantially a constant rate within the predetermined pressuredifferential range.

41. The invention of claim 1 wherein said power piston means includes avalve arrangement nomially open to communicate the chamber on one sideof said power piston with said piston means in the chamber on the otherside of said power piston, but which valve arrangement closes upontensioning the fishing string to compress the hydraulic fluid in thechamber.

42. The invention of claim l'including check valve means in said pistonmeans for communicating fluid across said piston means.

43. The invention of claim 19 wherein said power piston means includes avalve arrangement normally open to communicate the chamber on one sideof said power piston with said piston means in the chamber on the otherside of said power piston, but which valve arrangement closes upontensioning the fishing string to compress the hydraulic fluid in thechamber.

44. The invention of claim 19 including check valve means in said pistonmeans for communicating fluid across said piston means.

45. The invention of claim 36 wherein said power piston means includes avalve arrangement normally open to communicate the chamber on one sideof said power piston with said piston means in the chamber on the otherside of said power piston, but which valve arrangement closes upontensioning the fishing string to compress the hydraulic fluid in thechamber.

46. The invention of claim 36 including check valve means in said pistonmeans for communicating fluid across said piston means.

1. In a hydraulic fishing jar adapted to be run into a well on a fishingstring and connected to a fish in the well bore: a. inner and outertelescopically interengaged bodies; b. means defining between saidbodies a hydraulic fluid chamber; c. power piston means in the chamberoperable upon tensioning the fishing string for telescopic movement ofsaid bodies to compress and apply a predetermined force to the hydraulicfluid in the chamber; d. therebeing by-pass flow passage means in one ofsaid bodies; e. a valve member in the chamber for normally closing offone end of the by-pass flow passage means from the compressed fluid inthe chamber and shiftable to open so that compressed hydraulic fluid isreleased to the by-pass flow passage means; f. piston means includingsubstantially constant flow by-pass means to transfer the compressedhydraulic fluid in the chamber across said piston means and thereby moveit in the fluid chamber at substantially a constant rate to engage andmove said valve member to open the by-pass flow passage means at one endto the compressed hydraulic fluid; g. said piston means including valvemeans normally closing off the other end of the by-pass flow passagemeans and shiftable to open so that hydraulic fluid is released from thechamber above said piston means; h. means on one of said bodies to movesaid piston valve means and open the other end of the by-pass flowpassage means when said valve member is moved to open one end of theby-pass flow passage means to the compressed hydraulic fluid; and i.hammer and anvil means on said bodies movable into engagement when saidvalve member and piston valve means open the by-pass passage means tothe chamber across said piston means.
 2. The invention of claim 1wherein said piston means includes seal means sealably and slidablyengaged in the chamber to provide cross sectional areas of differentsize on said piston means responsive to the compressed hydraulic fluidin the chamber for transfer thereof across said piston means.
 3. Theinvention of claim 2 wherein said cross sectional areas are of apredetermined relationship for controlling the compressed hydraulicfluid pressure differential across said piston means in the chamberacting to move said piston means.
 4. The invention of claim 2 whereinsaid piston means is an annular member having top and bottom ends andwherein the cross sectional area defined by said seal means adjacentsaid bottom piston end is smaller than the cross sectional area definedby said seal means adjacent said top piston end.
 5. The invention ofclaim 1 including annular seat means formed on said piston valve meansand said piston means for seating said piston valve means on said pistonmeans.
 6. The invention of claim 1 including resilient means normallyurging said piston valve means into sealing engagement with said pistonmeans until said means on one of said bodies engages said piston valvemeans.
 7. The invention of claim 1 wherein said means on one of saidbodies at one end thereof forms seat means for said valve member.
 8. Theinvention of claim 7 including resilient means normally urging saidvalve member into sealing engagement with said seat meAns until saidpiston means moves said valve member off said seat means.
 9. Theinvention of claim 1 including resilient means in the chamber urgingsaid piston means away from said valve member and yieldable as saidpiston means moves to engage said valve member.
 10. The invention ofclaim 9 wherein said resilient means urging said piston means away fromsaid valve member also engages said power piston and is yieldable uponmovement of said piston means relative to said power piston.
 11. Theinvention of claim 1 wherein said means defining the hydraulic fluidchamber comprises upper and lower seal means between said bodies, one ofsaid seal means being a floating piston for compensating for thepressure of fluid in the well.
 12. The invention of claim 1 wherein saidvalve member is slidably and sealably carried by said inner body. 13.The invention of claim 1 wherein said piston valve means is slidably andsealably carried by said inner body.
 14. The invention of claim 1wherein said piston means is slidably and sealably carried in saidchamber.
 15. The invention of claim 1 wherein said by-pass flow passagemeans is formed in said inner body;
 16. The invention of claim 2 whereinone of said cross sectional areas is defined by seal means between saidpiston valve means and inner body and seal means between said pistonmeans and outer body, and the other of said cross sectional areas isdefined by seal means between said piston means and outer body and sealmeans between said piston means and inner body.
 17. The invention ofclaim 2 wherein said cross sectional areas are of a predeterminedrelationship for maintaining the compressed hydraulic fluid pressuredifferential across said piston means within a predetermined range. 18.The invention of claim 1 wherein said substantially constant flowby-pass means, includes substantially constant flow regulator meanswhereby the compressed hydraulic fluid moves therethrough atsubstantially a constant rate within the predetermined pressuredifferential range.
 19. In a hydraulic fishing jar adapted to be runinto a well on a fishing string and connected to a fish in the wellbore: a. inner and outer telescopic bodies; b. means includinglongitudinally spaced seals defining between said bodies a hydraulicfluid chamber; c. power piston means including an annular piston carriedby one of said bodies and shiftable longitudinally in said chamber bythe other of said bodies upon tensioning the fishing string fortelescopic movement of said bodies to compress and apply a predeterminedforce to the hydraulic fluid in the chamber; d. therebeing by-pass flowpassage means in one of said bodies; e. a valve member in the chamberfor normally closing off one end of the by-pass flow passage means fromthe compressed fluid in the chamber and shiftable to open so thatcompressed hydraulic fluid is released to the by-pass flow passagemeans; f. piston means including substantially constant flow by-passmeans to transfer the compressed hydraulic fluid in the chamber acrosssaid piston means and thereby move it in the fluid chamber atsubstantially a constant rate to engage and move said valve member toopen the by-pass flow passage means at one end to the compressedhydraulic fluid; g. said piston means including valve means normallyclosing off the other end of by-pass flow passage means and shiftable toopen so that hydraulic fluid is released from the chamber above saidpiston means; h. means on said inner body to move said piston valvemeans and open the other end of the by-pass flow passage means when saidvalve member is moved to open one end of the by-pass flow passage meansto the compressed hydraulic fluid; and i. hammer and anvil means on saidbodies movable into engagement when said valve member and piston valvemeans open the by-pass passage means to the chamber across said pistonmeans.
 20. The invention of claim 19 wherein said piston means includesseal meaNs sealably and slidably engaged in the chamber to provide crosssectional areas of different size on said piston means responsive to thecompressed hydraulic fluid in the chamber for transfer thereof acrosssaid piston means.
 21. The invention of claim 20 wherein said crosssectional areas are of a predetermined relationship for controlling thecompressed hydraulic fluid pressure differential across said pistonmeans in the chamber acting to move said piston means.
 22. The inventionof claim 21 wherein said piston means is an annular member having topand bottom ends and wherein the cross sectional area defined by saidseal means adjacent said bottom piston end is smaller in size than thecross sectional area defined by said seal means adjacent said top pistonend.
 23. The invention of claim 19 including annular seat means formedon said piston valve means and said piston means for seating said pistonvalve means on said piston means.
 24. The invention of claim 19including resilient means normally urging said piston valve means intosealing engagement with said piston means until said means on said innerbody engages said valve means.
 25. The invention of claim 19 whereinsaid means on said inner body at one end thereof forms seat means forsaid valve member.
 26. The invention of claim 25 including resilientmeans normally urging said valve member into sealing engagement withsaid seat means until said piston means moves said valve member off saidseat means.
 27. The invention of claim 19 including resilient means inthe chamber urging said piston means away from said valve member andyieldable as said piston means moves to engage said valve member. 28.The invention of claim 20 wherein said valve member is slidably andsealably carried by said inner body.
 29. The invention of claim 27wherein said resilient means urging said piston means away from saidvalve member also engages said power piston and is yieldable uponmovement of said piston means relative to said power piston.
 30. Theinvention of claim 19 wherein said piston valve means is slidably andsealably carried by said inner body.
 31. The invention of claim 19wherein said piston means is slidably and sealably carried in saidchamber.
 32. The invention of claim 19 wherein the by-pass flow passagemeans is formed in said inner body.
 33. The invention of claim 20wherein one of said cross sectional areas is defined by seal meansbetween said piston valve means and inner body and seal means betweensaid piston means and outer body, and the other of said cross sectionalareas is defined by seal means between said piston means and outer bodyand seal means between said piston means and inner body.
 34. Theinvention of claim 20 wherein said cross sectional areas are of apredetermined relationship for maintaining the compressed hydraulicfluid pressure differential across said piston means within apredetermined range.
 35. The invention of claim 19 wherein saidsubstantially constant flow by-pass means, includes substantiallyconstant flow regulator means whereby the compressed hydraulic fluidmoves therethrough at substantially a constant rate within thepredetermined pressure differential range.
 36. In a well bore fishingstring hydraulic fishing jar having inner and outer telescopicallyinterengaged bodies with a hydraulic fluid chamber therebetween andpower piston means in the chamber to compress and apply a predeterminedforce to the hydraulic fluid in the chamber upon tensioning the fishingstring for telscopic movement of the bodies, the improvement comprising:a. therebeing by-pass flow passage means in one of the bodies; b. avalve member in the chamber for normally closing off one end of theby-pass flow passage means from the compressed fluid in the chamber andshiftable to open so that compressed hydraulic fluid is released to theby-pass flow passage means; c. piston means including substantiallyconstant flow by-pass means to transfer the comPressed hydraulic fluidin the chamber across said piston means and thereby move it in the fluidchamber at substantially a constant rate to engage and move said valvemember to open the by-pass flow passage means at one end to thecompressed hydraulic fluid; d. said piston means including valve meansin the chamber normally closing off the other end of the by-pass flowpassage means and shiftable to open so that hydraulic fluid is releasedfrom the chamber above said piston means; and e. hammer and anvil meanson said bodies movable into engagement when said valve member and pistonvalve means open the by-pass passage means to the chamber across saidpiston means.
 37. The invention of claim 36 wherein said piston meansincludes seal means sealably and slidably engaged in the chamber toprovide cross sectional areas of different size on said piston meansresponsive to the compressed hydraulic fluid in the chamber for transferthereof across said piston means.
 38. The invention of claim 37 whereinone of said cross sectional areas is defined by seal means between saidpiston valve means and inner body and seal means between said pistonmeans and outer body, and the other of said cross sectional areas isdefined by seal means between said piston means and outer body and sealmeans between said piston means and inner body.
 39. The invention ofclaim 37 wherein said cross sectional areas are of a predeterminedrelationship for maintaining the compressed hydraulic fluid pressuredifferential across said piston means within a predetermined range. 40.The invention of claim 36 wherein said substantially constant flowby-pass means, includes substantially constant flow regulator meanswhereby the compressed hydraulic fluid moves therethrough atsubstantially a constant rate within the predetermined pressuredifferential range.
 41. The invention of claim 1 wherein said powerpiston means includes a valve arrangement normally open to communicatethe chamber on one side of said power piston with said piston means inthe chamber on the other side of said power piston, but which valvearrangement closes upon tensioning the fishing string to compress thehydraulic fluid in the chamber.
 42. The invention of claim 1 includingcheck valve means in said piston means for communicating fluid acrosssaid piston means.
 43. The invention of claim 19 wherein said powerpiston means includes a valve arrangement normally open to communicatethe chamber on one side of said power piston with said piston means inthe chamber on the other side of said power piston, but which valvearrangement closes upon tensioning the fishing string to compress thehydraulic fluid in the chamber.
 44. The invention of claim 19 includingcheck valve means in said piston means for communicating fluid acrosssaid piston means.
 45. The invention of claim 36 wherein said powerpiston means includes a valve arrangement normally open to communicatethe chamber on one side of said power piston with said piston means inthe chamber on the other side of said power piston, but which valvearrangement closes upon tensioning the fishing string to compress thehydraulic fluid in the chamber.
 46. The invention of claim 36 includingcheck valve means in said piston means for communicating fluid acrosssaid piston means.